CN1838373A - Ultra-high voltage mercury lamp - Google Patents

Abstract

The present invention provides an ultra-high pressure mercury lamp in which blackening and deformation of an electrode generated in a light emitting tube is suppressed, having long life of use, with suppressed flicker. This is the ultra-high pressure mercury lamp in which a pair of electrodes are opposed and arranged in the light emitting tube, in which 0.15 mg/mm<SP>3</SP>or more of mercury is sealed in as a light emitting material, and in which a coil part is formed by winding a conductive wire of a prescribed length around the tip part of an electrode shaft part of the pair of the electrodes which carries out a negative electrode action, and in the coil part, a proportion of a contact area of the conductive wire and the shaft part per a unit length in the shaft direction is the maximum in the rear end part of the coil part, and a part in which the proportion of the contact area is small is formed at least in one part in front of the rear end part.

Description

Ultra High Pressure Mercury Lamp

technical field

The present invention relates to a projection device such as a liquid crystal display device or a DLP (Digital Optical Processor) using a DMD (Digital Micromirror Device), in which mercury of 0.15 mg/mm3 or ^more is encapsulated in a light-emitting tube and the mercury Ultra-high pressure mercury lamp with vapor pressure above 150 atmospheres.

Background technique

In liquid crystal projectors or projection projection devices represented by DLP using DMD, since it is required to have uniform and sufficient color rendering and to illuminate images for rectangular screens, it is used in light sources Metal halide lamps in which mercury or metal halides are encapsulated. Recently, this kind of metal halide lamp has been developed towards further miniaturization and point light source, and halogen lamps with extremely small electrode spacing have also been applied.

Against such a background, recently, instead of a metal halide lamp, a lamp having a mercury vapor pressure as high as never before, for example, 150 atmospheres or more, has been proposed at the time of lighting. By increasing the mercury vapor pressure in this way, it is possible to further increase the light output while suppressing (reducing) the spread of arc light. Such ultra-high pressure mercury lamps are disclosed in Patent Document 1 and Patent Document 2, for example.

According to the mercury lamp disclosed in the above-mentioned document, a pair of electrodes are oppositely arranged in the luminous tube having a spherical light-emitting part in the central part, and mercury as a luminescent substance of 0.15 mg/mm ^or more is encapsulated in the inner space of the luminous tube, and simultaneously, in order to perform halogen cycle, also encapsulated with a specified amount of halogen gas.

In such ultra-high pressure mercury lamps, for example, as shown in Patent Document 3, in order to facilitate the transition from glow discharge to arc discharge when lighting is started, the coil portion wound with lead wire near the electrode tip is often exposed to discharge space.

[Patent Document 1] JP-A-2-148561

[Patent Document 2] JP-A-6-52830

[Patent Document 3] JP-A-2001-319617

Contents of the invention

In recent years, due to the strong demand for miniaturization and enhanced light output, the tube wall load of the ultra-high pressure mercury lamp used in the projection device tends to be higher and higher, and the distance between the electrode and the inner wall of the luminous tube tends to be getting shorter and shorter. In such an ultra-high pressure mercury lamp, there is a problem that when a direct current is used to illuminate the lamp lighting device at the initial stage of start-up, tungsten, which is an electrode constituent material, will adhere to the coil part due to the discharge of the coil part during start-up. Near the inner wall of the luminous tube, resulting in the undesirable phenomenon that the luminous tube turns black.

In addition, the shape of the electrode is deformed, so that the required luminance and light emission length cannot be obtained, the service life is shortened, and flickering phenomenon is caused.

As described above, when the shape of the electrode is deformed, the light transmittance decreases due to flickering or blackening of the arc tube, and the luminous flux decreases due to an excessively short emission length, thereby shortening the service life.

In view of the above problems, the object of the present invention is to provide an ultra-high pressure mercury lamp, which can suppress the occurrence of blackening of the luminous tube and deformation of the electrodes, has a long service life, and can suppress flickering.

In order to solve the above-mentioned problems, in the ultra-high pressure mercury lamp of the present invention, a pair of electrodes are oppositely arranged in the luminous tube, and at the same time as a luminous substance, mercury of 0.15 mg/mm ^or more is encapsulated, and the electrode shaft portion that acts as a cathode in the above-mentioned pair of electrodes A coil portion is formed by winding a wire with a predetermined length, and it is characterized in that: in the coil portion, the ratio of the contact area of the wire and the shaft portion to the unit length in the axial direction is behind the coil portion The end portion is the largest, and a portion having a relatively small contact area ratio is formed at least in a portion before the rear end portion.

Here, it is preferable that the wire is tightly wound around the rear end of the coil portion, and a portion where the wire is loosely wound is formed in at least a part before the rear end.

In addition, it is preferable that a gap between adjacent conductive wires among the conductive wires at the front end of the coil portion is 0.05 to 0.3 mm.

Preferably, the contact area is increased by interposing a metal member different from the lead wire forming the coil portion between the shaft portion and the lead wire.

Moreover, it is preferable that the said metal member is formed with the 2nd lead wire.

In addition, it is preferable that the diameter of the second lead is smaller than the diameter of the lead.

In addition, the above-mentioned metal member is preferably composed of a sintered body.

In addition, it is preferable to increase the ratio of the contact area between the lead wire and the shaft portion by forming a groove on the surface of the shaft portion corresponding to the rear end portion of the coil portion and fitting the lead wire into the groove.

When the present inventor studied the cause of the blackening of the luminous tube, he noticed that when the mercury lamp was switched from the glow discharge to the arc discharge immediately after the start of the mercury lamp, when the rear end of the coil part (abbreviated as "rear end") was formed When the starting point is discharged, the current will concentrate on the rear end of the coil part.

In addition, it was found that the phenomenon of blackening occurs precisely because the current is concentrated at the rear end of the coil portion.

It was also found that the failure to obtain the desired luminous length and the occurrence of light flickering were also caused by the deformation of the electrode due to the deposition and growth of tungsten.

Here, regarding the above phenomenon, an example of a conventional ultrahigh pressure mercury lamp will be described in detail using FIG. 5 .

Fig. 5 is an enlarged view of the vicinity of an electrode root in a conventional ultra-high pressure mercury lamp. 8( a ) and ( b ) show the same structure, but in FIG. 8( a ) symbols are used to explain the structure, and in FIG. 8( b ) symbols are used to explain the reaction in the luminous tube. FIG. 8(c) is a further enlarged view of the vicinity of the coil portion 22 in FIG. 8(a). In this figure, 1 is an arc tube, 2 is an electrode, 21 is a shaft portion of the electrode, and 22 is a coil portion wound with a wire such as tungsten.

The inventors of the present invention conjectured the following reason for the shortening of the distance L accompanying the lighting.

At the initial stage of starting, when the ultra-high pressure mercury lamp is illuminated by passing a DC current, observe the discharge form for a few seconds at the beginning of starting with an oscilloscope and a video camera, and the following phenomena are found.

First, after insulation breakdown, start-up is achieved by arc discharge of tens of volts of mercury generated from the surface of the electrode as the cathode in the DC region, and then, after the mercury on the surface of the cathode is completely evaporated, glow discharge of several hundred volts is performed. By glow discharge, the electrode (hereinafter referred to simply as "cathode") 2 working as the cathode is sufficiently heated, and thermal electrons are easily released from the cathode 2, and transferred to thermal arc discharge of tens of volts. When glow discharge is performed, the discharge is performed so as to cover the entire cathode 2, and the current density increases at the sharp wedge-shaped gap K between the coil portion 22 and the shaft portion 21, and then enters an arc discharge.

Afterwards, when the thermal arc discharge is performed, if the current is concentrated in the gap K, the locally heated tungsten is scattered and evaporated radially from the surface. Since the ionization voltage of the evaporated tungsten is lower than that of mercury and inert gas, it is easily ionized by the arc e, and the arc e is guided from the rear end of the coil portion 22 to the inner surface of the nearest arc tube 1 .

As a result, as shown in the figure, the inner surface of the luminous tube 1 will contact or collide with the high-temperature arc e. For this reason, pits will be formed locally on the inner surface of the luminous tube 1. At the same time, as the structure of the luminous tube 1 The material quartz glass (SiO ₂ ) evaporates. The evaporated SiO ₂ is decomposed into Si and O by the discharge plasma, thereby oxidizing tungsten constituting the cathode, and as a result, tungsten oxide is evaporated from the cathode 2 . When the tungsten oxide is transported to the rear end of the coil, the W accumulation shown by the dotted line is formed by the deoxidation reaction, and the distance D is further shortened.

It should be considered that this phenomenon will occur with a certain probability when the mercury lamp is started, therefore, it will lead to the accumulation of tungsten, and through the repetition of these reactions, it will lead to continuous growth and deposition until it contacts the inner surface of the luminous tube 1.

In addition, the present inventors also found that the following phenomena cause disadvantages.

In one case, the evaporated tungsten oxide is also transported to a portion other than the rear end of the cathode coil portion, such as the front end of the cathode, where it recrystallizes to form protrusions. When the protrusion grows between the electrodes, the desired light emission length suitable for the optical system cannot be obtained. In addition, since the discharge arc loss between the electrodes becomes smaller, the lamp voltage becomes lower. Therefore, a general discharge lamp stabilizer controls the current amount to a specified current according to the lamp voltage. If the lamp voltage is lower than the stable lighting , the input electric power is lower than desired for lighting. In this case, since the electric power of the lamp becomes lower, the luminous efficiency will be further reduced.

To make matters worse: There are also instances where multiple protrusions are present, at which point the bright spot of the arc will move between the fronts of the protrusions, causing flickering in the light output.

The present inventors have found that if the discharge arc generated from the rear end of the coil portion can be suppressed, the current concentration generated simultaneously with the discharge can also be suppressed there, thereby avoiding the evaporation of the quartz glass constituting the luminous tube. As a result, it is possible to avoid occurrence of the above phenomenon.

Invention effect

According to the ultra-high pressure mercury lamp of the present invention, in the coil portion, the rear end portion including the rear end thereof has a larger contact area with the lead wire than the front end, and the heat conduction from the lead wire to the shaft portion is good, so it is possible to avoid The heat generates a high temperature in the coil portion. In addition, in front of the rear end, where the contact area between the wire and the shaft is small, since heat conduction from the shaft to the coil is suppressed, the temperature rises, and thermal arcing tends to be formed there. As a result, thermal arcing occurs where the contact area of the lead wire and the shaft portion is small, and is less likely to occur from the rear end portion of the coil portion.

In this way, by reducing the arc discharge generated from the rear end of the coil portion, it is possible to avoid the phenomenon that tungsten, which is an electrode-forming substance, adheres to the inner wall of the arc tube near the coil portion to cause the arc tube to become black. The formed thermal arc discharge is far away from the inner wall of the luminous tube, thereby inhibiting the evaporation of quartz glass and avoiding the resulting cathode oxidation.

As a result, problems such as lowering of light transmittance due to blackening of the luminous tube, shortening of service life due to reduction of light beam due to too short luminous length, and occurrence of flickering can be effectively prevented.

In addition, in the above-mentioned ultra-high pressure mercury lamp, by setting the gap xmin. of the above-mentioned coil part between 0.05-0.3 mm, the occurrence position of thermal arc discharge can be well controlled with the effect of the hollow effect. At least one gap forming the above-mentioned range is provided at a place other than the rear end of the coil portion, thereby more reliably avoiding arc discharge from the rear end of the coil that causes the above-mentioned problem. The gap in the above range can be provided anywhere except the rear end of the coil, but is more desirable at the front end of the coil.

In addition, the contact area between the electrode shaft and the coil can be reduced by enlarging the gap between the coil and the electrode shaft at the coil front end, or conversely, by filling the gap between the coil and the electrode shaft at the coil rear end side. The gap to increase the contact area between the electrode shaft and the coil, or either of these two methods, delays the heat diffusion from the front end of the coil to the electrode shaft, making it easy to reach the temperature transferred from glow discharge to arc discharge. As a result, the origins of transition to thermal arc discharge can be concentrated on the front end side of the coil portion, thereby reliably preventing the rear end of the coil from becoming a discharge origin during thermal arc discharge.

Description of drawings

Fig. 1 is a cross-sectional view of an ultra-high pressure mercury lamp illustrating a first embodiment of the present invention.

2 is an enlarged view of the cathode, wherein (a) is a front view, and (b) is a cross-sectional view including the central axis.

Fig. 3 is an enlarged axial sectional view showing the vicinity of the coil portion of the cathode, illustrating a second embodiment of the cathode of the present invention.

Fig. 4 is for explaining a third embodiment of the cathode of the present invention, wherein (a) is a front view, and (b) is a cross-sectional view including the central axis.

5 is a diagram illustrating a fourth embodiment of the cathode of the present invention, wherein (a) is a front view, and (b) is a cross-sectional view including the central axis.

Fig. 6 is a sectional view including the central axis of the cathode for explaining another embodiment of the present invention.

Fig. 7 is a sectional view including the central axis of the cathode for explaining another embodiment of the present invention.

FIG. 8 is an enlarged view showing a root portion of an electrode in the prior art.

Detailed ways

Fig. 1 is a cross-sectional view illustrating an ultra-high pressure mercury lamp of a first embodiment.

The ultra-high pressure mercury lamp 100 has a luminous tube 1 made of quartz glass, for example. The luminous tube 1 has a substantially spherical luminous portion 11 and rod-shaped sealing portions 12 , 12 connected to both ends of the luminous portion 11 . A cathode 2 and an anode 3 are arranged opposite to each other in the inner space S of the luminous tube 1 . The cathode 2 includes a shaft portion 21 and a coil portion 22 formed by winding a wire W around the shaft portion 21 , and the anode 3 includes a shaft portion 31 and a body portion 32 provided at a front end of the shaft portion 31 .

Metal foils 4 , 4 for power supply made of molybdenum, for example, are embedded in the sealing portions 12 , 12 of the arc tube 1 and sealed. One end of these metal foils 4,4 is welded together with the base end portions 211,311 of the shaft portions 21,31 to realize electrical connection, and the other end is connected with the external wire 5, 5 soldered together for electrical connection.

Mercury, halogen gas and inert gas are encapsulated in the luminous tube 1 .

Mercury is used to obtain the necessary visible light wavelengths, such as 360-780nm radiated light. In order to make the mercury vapor pressure at the time of lighting reach 150 atmospheres or more, mercury of 0.15 mg/mm ³ or more should be encapsulated. The amount of mercury varies with temperature conditions, and the amount of mercury can be appropriately changed according to the desired mercury vapor pressure.

As for the inert gas, in order to improve lighting startability, argon gas of 5 to 50 kPa, for example, 13 kPa may be encapsulated.

Halogen is encapsulated in the form of compounds of iodine, bromine, chlorine, etc. and mercury or other metals, and the encapsulated amount ranges from 10 ^-6 to 10 ^-1 μmol/mm ³ , for example, 3.0×10 ^-4 μmol/mm ³ . Its function is also to prolong the service life by utilizing the halogen cycle, but its main purpose is to prevent devitrification of the arc tube in an extremely small discharge lamp with high internal pressure like the discharge lamp of the present invention.

FIG. 2 shows an enlarged view of the cathode of the ultra-high pressure mercury lamp shown in FIG. 1 . FIG. 2( a ) shows a front view, and FIG. 2( b ) is an enlarged view of main parts in a section including the central axis L. As shown in FIG. In FIG. 2, the same parts as those in FIG. 1 are given the same reference numerals.

The coil portion 22 of the cathode 2 is formed, for example, by winding a wire W made of linear tungsten tightly around the outer peripheral surface of the electrode shaft portion 21 . The winding method is such that a gap is left between adjacent conductive wires W at the front end portion 221 of the electrode front side of the coil portion 22, and the distance is reduced from the front to the rear. In the rear end portion 222 including the rear end 22a, it is tightly wound so that the interval between the wires W becomes almost zero.

Here, the "rear end 22a" of the coil part refers to the rearmost end of the wire W constituting the coil part 22 located on the electrode shaft part 21, and the "rear end part 222" refers to a predetermined length including the above-mentioned coil part rear end 22a. area, and it is appropriately set to 20 to 60% of the entire length of the coil portion 22 . The “front end portion 221 ” of the coil portion refers to an area of a predetermined length including the front end of the conductive wire W, which is an area other than the rear end portion 222 .

In this way, the winding interval of the lead wire W is different along the length direction of the shaft portion, and the ratio of the contact area of the lead wire W and the shaft portion 21 per unit length is the largest at the rear end portion 222. Therefore, compared with other portions, At the rear end portion 222, heat generated during glow discharge is easily conducted to the shaft portion 21, so that heat dissipation can be facilitated. On the other hand, since the front end portion 221 of the coil portion 22 has a small contact area with the electrode shaft portion 21 , less heat is conducted to the shaft portion 21 and the temperature in the coil portion 22 is higher.

In this way, in the coil portion 22, the rear end portion 222 has a lower temperature and there is a higher temperature portion in front of it, so the position where thermal arc discharge occurs can be shifted to a coil other than the rear end portion 222. The front end portion 221 of the portion can reduce the probability of thermal arc discharge occurring at the rear end portion 222 .

As a result, by reducing the thermal arc discharge generated from the rear end portion 222 of the coil portion, it is possible to prevent the tungsten, which is an electrode constituent material, from adhering to the inner wall 11A of the light emitting portion in the vicinity of the coil portion 22 and causing the light emitting portion 11 to be blackened. The thermal arc discharge is isolated from the inner wall 11A of the luminous part, so that evaporation of the quartz glass constituting the luminous tube 1 and oxidation of the cathode 2 caused by it can also be suppressed.

Based on the above, in the front end portion 221 of the coil portion 22, it is preferable that there is a portion where the gap xmin. between adjacent conductive wires W is 0.05 mm or more, for example, 0.05 to 0.5 mm. In this way, by setting the gap xmin. in the range of 0.05 to 0.3 mm, the heating effect by the so-called hollow effect (described later) can be obtained, and the temperature of the front end portion 221 of the coil portion 22 can be effectively raised. Therefore, Easier to be the starting point for thermal arc discharges.

At this time, it is preferable that the gap between the conductive wires W is smaller than 0.05 mm at the rear end portion 222 of the coil portion 22 . In this way, the warming effect caused by the hollow effect is not produced. Therefore, combined with the fact that the temperature of the front end portion 221 rises, it is possible to effectively prevent the generation of thermal arc discharge at the rear end portion 222 .

Next, the hollow effect will be briefly described.

Generally speaking, if the distance between the wires in the cathode coil part is reduced, the two negative glow regions on the coil surface will overlap, and the distance between the cathode drop region and the distance between the negative glow regions will be reduced respectively. In normal discharge, if the value of the discharge voltage between the electrodes is kept at the same value, almost all of the above-mentioned discharge voltage is applied to the cathode drop region, thereby increasing the electric field in the cathode drop region. In addition, a further increase in ion density will further increase the ion current density between the cathodes. In addition, by shortening the distance of the descending part of the cathode, for the energy obtained by the acceleration of the electrons flying out of the cathode on the way, the number of collisions in the dark region of the cathode is reduced, so the proportion of the loss can be reduced. As a result, electrons will fly into the negative glow region with high energy, thereby promoting ionization and excitation in the negative glow region. Since the light intensity in the negative glow area will also increase, the ultraviolet rays contained in the light will collide with the cathode, thereby promoting the cathode to emit photoelectrons. As a result, the glow discharge current density also increases and the surrounding coil temperature rises, enabling a faster transition to hot arc discharge than other cathode sites.

On the other hand, since there is no gap in the coil of the cathode, its function is almost the same as that of a flat plate cathode, therefore, the distance of the cathode drop region on the surface of the coil is not reduced, and therefore, the above-mentioned effect of promoting photoelectron emission cannot be obtained. . Therefore, the glow discharge current density is low, and the coil temperature cannot be raised.

In order to manufacture such an electrode that can locally obtain the hollow effect in the electrode length direction, for example, the following method can be used to manufacture the electrode.

For example, a wire made of tungsten or the like is wound several times at regular intervals, and further wound thereafter so that the wires are closely connected to each other to form a coil molded body. Put it on the shaft made of tungsten, and fix it by riveting or the like. Alternatively, the lead wire may be directly wound around the electrode shaft and fixed by riveting as well.

If it is necessary to partially expand or change the coil pitch, the feeding amount of the electrode shaft or the wound coil wire can be program-controlled by a lathe, so that it can be freely changed to obtain the desired coil pitch. In addition, after coils are wound at equally spaced pitches, tensile stress can be applied to one end or part of the coils, thereby stretching and enlarging partial pitches. If this stress is also used as the stress for cutting the coil end, man-hours can be reduced. In addition, among the coils wound at equal intervals, the pitch can also be selectively increased locally by selecting and applying pressure such as caulking to the local area.

Data relating to the cathode are given below.

The diameter of the shaft portion 21 is in the range of φ0.3 mm to φ3 mm, for example, φ0.8 mm, and its volume is in the range of 4 mm ³ to 40 mm ³ , for example, 23 mm ³ . In addition, the surface area is 10 mm ² to 45 mm ² , for example, 20 mm ² , and the overall length is 7 mm to 20 mm, for example, 10 mm. In the shaft portion 21 , a portion equivalent to half of the total length is embedded in the closing portion 12 , and the remaining half is exposed to the internal space S. As shown in FIG. The diameter of the linear tungsten constituting the lead wire W is 0.2 mm to 0.6 mm, for example 0.25 mm, and the number of turns around the shaft portion 21 is about 2 to 10 turns, for example 5 turns. The pitch of the front end portion 221 is 0.2 mm to 2 mm, for example, 0.3 mm.

In addition, it is preferable to use tungsten with a purity of 99.99% or higher for the shaft and the wire.

According to the ultra-high pressure mercury lamp of the present invention as described above, in the rear end portion including the rear end of the coil portion, since the proportion per unit length of the contact area with the electrode shaft portion is larger than other portions, a glow discharge occurs. The heat in the rear end is easily conducted to the shaft, so that heat dissipation can be promoted and the temperature of the rear end can be kept low. At the front end portion of the coil portion where the temperature is relatively high, thermal arc discharge can occur at a high probability.

As a result, the arc discharge generated from the rear end of the coil part can be reduced, thereby avoiding the phenomenon that the tungsten as the electrode constituent material adheres to the inner wall of the luminous tube near the coil part and causes the luminous tube to become black. The thermal arc discharge formed immediately afterwards is isolated from the inner wall of the luminous tube, which can inhibit the evaporation of quartz glass and avoid the resulting cathode oxidation.

In addition, if a part where the distance between the wires is in the range of 0.05 to 0.3 mm is formed at the front end of the coil part, since the heating effect due to the hollow effect can be obtained, the occurrence of thermal arc discharge can be concentrated on the front end of the coil part. part, thereby avoiding arc discharge at the rear end and preventing current from concentrating at this position.

Next, a second embodiment of the present invention will be described. Fig. 3 separately shows the cathode related to the second embodiment of the present invention, wherein (a) is a front view and (b) is a sectional view. The structures other than the cathode are the same as those of the above-mentioned first embodiment, so their descriptions are omitted.

The conductive wire W forms a gap between adjacent conductive wires, and is wound at a constant pitch throughout the entire coil portion 22 . That is, in the present embodiment, the area ratio per unit length where the lead wire W is in contact with the electrode shaft portion 21 is almost the same throughout the coil portion 22 .

On the outer peripheral surface of the electrode shaft portion 21 , the second conductive wire 23 is wound at a predetermined distance from the rear end 22 a of the coil portion 22 to the front. The second lead wire 23 is made of a high-melting point metal such as tungsten wire, and the range of the installed portion accounts for 20 to 60% of the entire length of the coil portion 22 . In addition, it is preferable that the second wire is thinner than the wire constituting the coil part as in this embodiment, so that the size of the coil will not be increased excessively, and the advantage is that the hindrance of the coil to the use of the emitted light beam emitted from between the electrodes can be suppressed to a minimum. limit. Specifically, when the diameter of the wire on the side of the coil portion 22 is 0.25 mm, the diameter is about 0.1 mm.

This second lead wire 23 is set in such a way that it can be filled in the gap while being in contact with the lead wire W constituting the coil portion 22. In this way, the lead wire W contacts the electrode shaft portion 21 through the lead wire 23, thereby actually The contact area is enlarged.

Like this, because by winding the 2nd lead wire on the electrode shaft part 21, the contact area between the electrode shaft part 21 and the coil part 22 is expanded by the 2nd lead wire 23, therefore, can make the rear end part 222 of the coil part 22 The heat is quickly transferred to the shaft portion 21 to facilitate heat dissipation there. Therefore, the temperature of the rear end portion 222 of the coil portion 22 is less likely to rise than that of the portion in front of which the second lead wire 23 is not provided, so that the occurrence of thermal arc discharge can be avoided.

As a result, the same effects as those of the first embodiment described above can be obtained.

Next, a third embodiment of the present invention will be described. Fig. 4 alone shows the cathode related to the third embodiment of the present invention, wherein (a) is a front view and (b) is a cross-sectional view. Here, the structure other than the cathode is the same as that of the above-mentioned first embodiment, so the description thereof will be omitted.

The conductive wire W is wound at a constant pitch throughout the entire coil portion 22 with gaps formed between adjacent conductive wires. In this way, the ratio of the area per unit length where the lead wire W is in contact with the electrode shaft portion 21 is almost constant throughout the entire coil portion 22 .

On the outer peripheral surface of the electrode shaft portion 21 , a tungsten sintered body 24 having a predetermined length is provided axially forward from a rear end portion 222 of the coil portion 22 . The sintered body 24 is formed by applying a mixture of tungsten powder and an appropriate amount of binder to a predetermined area, and then calcining at a high temperature (for example, 2000° C.) in a vacuum environment (for example, 6×10 ⁻⁵ Pa). By arranging the tungsten sintered body 24, the contact area of the wire W through the tungsten sintered body 24 and the electrode shaft portion 21 is actually increased, thereby promoting the transfer of heat in the glow arc to the electrode shaft portion 21. Therefore, in the glow arc, The temperature of this portion is less likely to rise than other portions where the tungsten sintered body 24 is not provided.

Fig. 5 shows alone the cathode related to the fourth embodiment of the present invention, wherein (a) is a front view and (b) is a cross-sectional view. Here, the structure other than the cathode is the same as that of the above-mentioned first embodiment, so the description thereof will be omitted.

In this embodiment, a stepped portion 21A having a smaller diameter at the front end and a larger diameter at the rear end is formed on the shaft portion 21 at a predetermined position, and a spiral shape is formed on the outer surface of the large diameter portion of the stepped portion 21A. slot 25.

The groove 25 has a semicircular cross-section in accordance with the diameter of the wire W, and its total length is 20 to 60% of the total length of the coil portion 22 .

The wire W is inserted into the groove 25 in such a way that the terminal part is almost coincident with the rear end 22a of the wire W, thereby forming an area of the rear end 222 of the coil part 22 that actually increases the distance between the wire W and the axis. The ratio of the contact area of the portion 21.

Like this, because on the electrode shaft part 21, the groove 25 that wire W fits is formed in the part corresponding to the rear end part 222 of the coil part 22, and the contact area is enlarged, therefore, the rear end part 222 of the coil part 22 can be made The heat is quickly transferred to the shaft portion 21, thereby promoting the heat dissipation there. Therefore, the temperature of the rear end portion 222 of the coil portion 22 is less likely to rise than that of the front portion thereof, thereby avoiding occurrence of thermal arc discharge.

In the above, although the description has been made based on the embodiment, the present invention should not be limited thereto and can be appropriately changed.

That is, according to the present invention, as long as the ratio of the contact area between the lead wire and the electrode shaft in the coil portion to the unit length of the shaft is maximized at the rear end including the rear end of the coil, and the rear end is excluded in the coil portion It is only necessary to form a portion having a smaller contact area than the rear end portion at least at a portion other than the rear end portion. The reason for this is that the position where thermal arc discharge occurs can be moved to the front side of the coil portion by at least partially providing a place at a portion other than the rear end portion of the coil portion at a temperature higher than the rear end portion. In this way, as a modification of the above-mentioned first embodiment, for example, as shown in FIG. 6, in the case of changing the pitch of the conductive wire W, if the winding is tightly wound at the rear end portion 222 of the coil portion, at least a part of the front portion thereof If there is a loosely wound part 223 on the top, it does not matter even if there is a tightly wound part at the front end. In this case, since a high-temperature portion is formed in the open-wrap portion 223 , thermal arc discharge is easily generated therefrom, and as a result, generation of thermal arc discharge from the rear end portion 222 can also be suppressed.

In addition, other components may be interposed between the lead wire W and the electrode shaft portion 21 as long as it is provided over the entire length of the coil portion 22 and heat can be uniformly conducted from the lead wire to the electrode shaft portion. For example, as shown in FIG. 7 , other coil members 26 or the like formed at constant pitches may be provided between the lead wire W and the electrode shaft portion 21 .

In addition, although the above-mentioned embodiments relate to DC lighting type ultra-high pressure mercury lamps, the present invention is not limited thereto, and it is also applicable to AC lighting type ultra-high pressure mercury lamps.

Next, experimental examples for confirming the effects of the present invention will be described.

First, a plurality of experimental lamps were manufactured according to the structure of FIG. 1 . In addition, the pitch of the coil portion was appropriately changed to produce a plurality of lamps related to the comparative example.

The basic specifications of the lamp are as follows.

The material of the luminous tube is quartz glass, the total length is 74mm, the maximum diameter of the luminous part is Φ10mm, the total length of the luminous part is 10mm, the internal volume is 66mm ³ , the diameter of the closed part is Φ6.5mm, and the length is 32mm.

The material of the shaft portion of the electrode on the cathode side is tungsten, the diameter is 0.8 mm, and the overall length is 11 mm.

At the large diameter portion at the front end of the anode, the maximum outer diameter is 1.8 mm, and the overall length is 3 mm. The shaft is made of tungsten, with an outer diameter of 0.8mm and a total length of 13mm.

A molybdenum foil with a thickness of 25 μm, a width of 2 mm, and a length of 14 mm was used for the metal foil, and a molybdenum rod with a diameter of Φ0.8 mm was used for the external guide rod.

In addition, 18 mg of mercury is encapsulated in the light emitting part.

The coil portion formed on the cathode side is wound with a tungsten wire with a wire diameter of Φ0.25 mm and a length of 1.0 mm. Starting from the front end of the coil part, the part that occupies 40% of the total length of the coil is defined as the front end of the coil part, and on the other hand, the part that occupies 40% of the total length of the coil from the rear end of the coil part is defined as the length of the coil part. rear end.

In this experimental example, according to the following Table 1, the distance between the wires was changed between 0 (zero, ie less than 0.05) to 3.0 mm, and n=3 lamps of various specifications were used for the ignition test. In the lighting test, the input of the lamp was 200W (the initial voltage was 80V, and the current was 2.5A), and the lamp was turned on for 5 minutes and turned off for 5 minutes, and this was repeated 500 times.

The following table summarizes the test results. The evaluation of blackening is based on the appearance of the blackened state of the root of the cathode after spotting is observed using a microscope. The ◎ symbol (double circle) indicates no blackening, and the ○ symbol (single circle) indicates a little blackening but The light transmittance is hardly affected, the △ symbol (triangle) indicates that the light transmittance is reduced by about half compared with the initial stage but still has light transmittance, and the × mark indicates that the light transmittance has almost disappeared due to blackening.

[Table 1] Specification light 1 light 2 light 3 light 4 light 5 lamp 6 Spacing between wires at the front end of the coil 0(<0.05) 0(<0.05) 0.3 0.05 0.1 0.3 Spacing between wires at the rear end of the coil 0.3 0(<0.05) 0.3 0(<0.05) 0(<0.05) 0(<0.05) evaluate After 100 clicks △ ○ ○ ○ ◎ ◎ After 300 clicks x △ △ ○ ◎ ◎ After 500 clicks x x x △ ○ ○

As shown in Table 1, significant blackening occurred in Lamp 1, and the light transmittance was almost lost after 300 times of lighting. Lamps such as Lamp 2 and Lamp 3 with the same gap in the entire coil portion (that is, conventional lamps) greatly reduce the light transmittance due to the influence of blackening after 300 times of extinguishing, and almost Loss of translucency. On the other hand, like lamp 4, in a lamp in which the distance between the wires at the rear end of the coil is almost 0 (zero) and a gap of 0.05 mm is formed at the front end, it can be seen that there is still sufficient transparency even after 300 times of lighting off. Lightening, the effect of darkening is greatly reduced. Moreover, after 500 times of extinguishing, the effect of blackening gradually appeared, but it still has light transmission and sufficient durability.

In addition, when the gap at the front end side of the coil is further enlarged to 0.1 mm and 0.3 mm, it is obvious from the results of lamp 5 and lamp 6 that the phenomenon of blackening does not appear after 300 times of extinguishing, and still remains after 500 times of extinguishing. Has sufficient light transmission.

The above results show that by setting the gap between the wires at the front end of the coil to 0.05 mm to 0.3 mm, and setting the gap between the wires at the rear end of the coil to less than 0.05 mm, the blackening phenomenon can be greatly reduced, so that the light-emitting tube The light transmittance is maintained at a high level.

In addition, inspection of the lighting conditions of the lamps in the above-mentioned experimental example revealed that, for lamps 4 to 6, no defects such as deposition of tungsten oxide on the tip of the electrode and shortening of the light emitting length occurred. In addition, tungsten oxide deposition and scintillation phenomena did not appear. Therefore, according to the present invention, it is possible to effectively prevent the movement of the arc bright point caused by the formation of a plurality of oxide protrusions in the conventional lamp.

In the above experimental examples, although a DC lighting lamp was used, for an AC discharge lamp, since one electrode acts as a cathode for alternate glow discharge, it is also applicable to an AC discharge lamp. .

Claims (8)

1. an extra-high-pressure mercury vapour lamp is oppositely arranged pair of electrodes in luminous tube, simultaneously as luminescent substance, is packaged with 0.15mg/mm ³Above mercury,

Play the leading section of the electrode axial region of cathodic process in described pair of electrodes, the lead formation coil portion by the coiling specific length is characterized in that,

In described coil portion, the contact area of described lead and described axial region is with respect to the ratio of the unit length of the axial length direction rearward end maximum at this coil portion,

On at least a portion before the described rearward end, form the less part of ratio of contact area.

2. extra-high-pressure mercury vapour lamp according to claim 1 is characterized in that, described coil portion is portion's lead of closely reeling in its back-end, and forms the part of the loose described lead of reeling at least a portion before this rearward end.

3. extra-high-pressure mercury vapour lamp according to claim 2 is characterized in that, the gap in the lead of described coil portion leading section between the adjacent wires is 0.05～0.3mm.

4. according to any described extra-high-pressure mercury vapour lamp in the claim 1～3, it is characterized in that,, increase contact area thus by establish and form the different metal parts of lead of described coil portion at folder between axial region and the lead.

5. extra-high-pressure mercury vapour lamp according to claim 4 is characterized in that described metal parts is made of the 2nd lead.

6. extra-high-pressure mercury vapour lamp according to claim 5 is characterized in that the diameter of described the 2nd lead is less than the diameter of described lead.

7. extra-high-pressure mercury vapour lamp according to claim 4 is characterized in that described metal parts is made of sintered body.

8. extra-high-pressure mercury vapour lamp according to claim 1 is characterized in that, forms groove by the surface that is equivalent to the coil portion rearward end in described axial region, and, make lead embed this groove, increase the ratio of the contact area of lead and axial region thus.

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